Separation of thiophenols from hydrophobic liquid mixtures



same.

Patented Dec. 5, 1944 SEPARATION OF THIOPHENOLS FROM HYDROPHOBIC-LIQUID. MIXTURES George W. Ayers, J12, and Meyer's. Agruss, Chicago; andRichmond T. BelltDeerfield, 111., assign'ors to The Purev Oil Company;Chicago, Ill-.,.

a corporation of Ohio No'Drawing. "Application June2'1, 1941,

' Serial No. 399,228

6; Claims.

This invention relates to a method for separate ing thiophenols fromhydrophobic liquidurnixr tures containing-thesame and is moreparticularly concernedwith a. method for separating thiophenols fromacid oils.

Mixtures of thiophenols, phenols and other oil-soluble weakly acidicorganic compounds bta ined from hydrocarbon. oils by extraction withcaustic alkali, are generally called acid oils. Acid oils may containsubstantial.quantities-of thiophenols, as well as 'alk-yl phenols andother organic acidic compounds such. as naphthenic acids and in somecases varyingamounts of polycyclic aromatic ring. phenolic compounds Theamount of thiophenols present in .a specific acid oil is dependent uponthe. composition of the original hydrocarbon oil and the treatmentv towhich the oil. has been subjected. The acid oils are usually obtained byextracting. cracked mineral oil distillates with strong. aqueous alkalimetal hydroxide solutions andthe acid oils. separated from the resultingextract by springing with su tabl acidic material. springing may beeffected. by adding sufficient acidic material to the aqueous alkalisolution to neutralize the Acid oils as thus preparedordinarily con'-tain undesirable alkyl mercaptans. Acid oils substantially free of alkylmercaptans -may be readily obtained. by steam stripping or' boiling theaqueous alkali solutions'prior to the springing operationi Thiophenolsin acid oils havebeen: separated from alkyl phenols in the'past'byextracting the acidoils with an organic'water insoluble solvent foralkyl phenols in the presence of aqueous solution of an alkali metalhydroxide i'nan amount approximately equivalentto the thiophenol contentof the acid oil. Under such conditions alkyl phenols preferentiallydissolve in the solvent. This method, however, does. not producesubstamtially pure thiophenols It. has now beendiscoveredthat substantiallypure thiophenolfractions and. substantially pure thiophenol compoundsmay be separatedirom acid oils which are substantially free of alkylmercaptans by precipitation with heavy metal salts.

It is an object of this invention to recover thiophenols from acid oilsin a substantially pure form.

It is another object of this invention to recover thiophenolssubstantially free of other weakly acidic organic compounds" and free ofv relatively high proportions of thiophenols.

each other from acid oils which are substantially free-of alkylmercaptans.

It'is still a further object of this invention to efllciently separatethiophenols from acid oils.-

Other objects and advantages will'be apparent from th following' moredetailed description.

As previously indicated, it has been found that thiophenols may beseparated from acid oils that are substantially free of alkyl mercaptansin a relatively pure state by precipitation with heavy metal salts" suchas salts of the heavy metalsof Groups 1, 2 and 4 of the periodic table.In order to avoid contamination with alkyl mercaptans, such materials arremoved from the aqueous alkaline solutions which have been employed toextract the acid oils from hydrocarbon oils; preferably by steamingand/or boiling; Those alkaline solutionswhich have been used a pluralityof times for the extraction of petroleum oil's'and: regenerated by steamstripping are preferred since these solutions ordinarily contain Whenheavy metal salts are added to acid oils obtained from such alkalisolutions, heavy metal'salts of thiophenols are formed and these salts,precipitatein a relatively pure form. This may be effected by simplyagitating the acid oils with aqueoussolutions or suspensions ofappropriate heavy metal salts, preferably aqueous solutions of salts ofthose heavy metals that are precipitated fromacidicsolutions withhydrogen sulfide. Heavy metal salts which have been found suitable forthis purpose include water soluble salts of mercury, silver. and lead.Particularly good results have. been. obtained with water soluble saltsof mercury. Suitable salts include mercuric cyanide, mercuric acetate,silver acetate, sllvernitrate and, lead. acetate.

After precipitation of the heavy metal salts of the thiophenols from theacid oil, the salts are separatedtherefromby filtration or other appropriate. means. These salts. may be further purified. by'fractionalcrystallization from an appropriate solvent such as. aqueousalcoholis olution. Thiophenols are then recovered from the heavy metalsalts thereof by dispersing, i. e., suspending or dissolving the heavymetal. thiophenolic salts: in. a suitablelliquid such as a lowboilingshydrocarbon liquid and acidifying the liquid as for example, bypassing hydrogen sulfide therethrough, which frees the thiophenols.Other acidifying agents can be used but best results areobtalned by theuse of an acid reagent which precipitates the heavy metal in the formsubsequently separated from the petroleum hy-.

drocarbon solvent by distillation. Individual thiophenols may beseparated from each other in the same or a subsequent distillation bycarethat the precipitates formed are of uniform composition and aresimple salts of individual thiophenols which are readily purified ascontrasted to precipitates obtained with other heavy metals which arecomplex mixtures of various thiophenol salts. It is exceedinglydifficult to obtain substantially pure thiophenols from the latterprecipitates.

The substantially pure thiophenols maybe employed as solubilitypromoters in aqueous alkali metal hydroxide solutions for enhancing theability of such solutions to extract mercaptans from petroleum oils.Pure thiophenols are also in] fractionation by virtue of difference inboiling point. It is, of course, apparent that the original acid oilsmay be fractionated prior to the precipitation therefrom of the heavymetal salts of thiophenols. In this way the phenolic heavy metal saltsmay be directly precipitated as substantially pure individual thiophenolcompounds.

In a specific example, acid oil obtained by aqueous alkali extraction ofa mixture of cracked and straight run Van Zandt and Schuler gasolineswas separated from the alkali extracting solution by acidification anddecantation. A portion of the acid oil was contacted with an equalvolume of 10% aqueous mercuric cyanide solution and the Whiteprecipitate of mercuric aromatic mercaptide separated by decantation andwashed with water. The washed precipitate was crystallized repeatedlyfrom hot 80% aqueous ethyl alcohol solution by simply cooling thesolution. The resulting material was identified as substantially puremercuric o-tolyl mercaptide. This material constituted more than half ofthe origina1 mercaptide precipitated. The purified white mercurico-tolyl mercaptide was suspended in heptane and hydrogen sulfide gaspassed through the suspension until precipitation of black mercuricsulfide was complete. This acidifies the thiophenol salts and frees thearomatic mercaptan which dissolves in the heptane. After washing withwater, the aromatic mercaptan-heptane solution layer was distilled ando-thiocresol recovered as a residue.

In another example, a separate portion of the same acid oil wasfractionally distilled and a fraction obtained, the boiling range ofwhich was close to theboiling point of o-thiocresol. O-thiocresol boilsat 194 C. and the boiling range of this fraction was 174 C. to 214 C.This narrow boiling fraction of the acid oil was treated with an aqueoussolution of mercuric cyanide to precipitate mercuric aromatic mercaptidein a manner similar to that described in connection with the treatmentof the first portion of acid oil. The precipitate was suspended inheptane, hydrogen sulfide passed through the suspension to precipitatemercuric sulfide and to free the aromatic mercaptan. The heptanesolution of aromatic mercaptide was then distilled to remove heptane.The residue from the distillation of the heptane layer was fractionallydistilled, yielding substantailly pure o-thiocresol.

The fractional crystallization steps which were carried out in theaforementioned procedures may be reduced in number or eliminated byemploying sufiiciently sharp fractionation of the acid oil prior to theprecipitation of the heavy metal salt.

While salts of thiophenols may be precipitated by the use of salts ofmetals other than those specified herein, it has been found that it isonly by the use of salts of the metals herein disclosed useful asadditives for enhancing the lubricating properties of minerallubricating oil and may also be employed as odorizing agents for naturalgas. In general, the purified thiophenols may be employed instead of thecorresponding hydroxy benzenes in many organic syntheses for thepreparation of sulfur containing compounds whereby sulfur from thesulfhydryl group, instead of oxygen from the hydroxy group, is presentin the final product.

The foregoing general description of the invention and the specificexample described are sufficient to enable one skilled in the art toappreciate its value. The invention is not limited to the specificexamples disclosed but is to be interpreted as broadly as the prior artpermits in view of the following claims.

What is claimed is:

1. The process of separating substantially pure thiophenols from acidoils containing the same which are substantially free of alkylmercaptans comprising contacting the acid oils with watersoluble saltsof metals selected from the group consisting of mercury, lead and silverwhereby to precipitate metal salts of thiophenols, separating saidprecipitated salts, dispersing the separated salts in a hydrocarbonliquid boiling below the boiling point of thiophenol, treating thedispersed salts with sufiicient hydrogen sulfide to convert dispersedsalts to an oily layer of substantially pure thiophenols dissolved inthe hydrocarbon liquid and to precipitate metal sulfide and separatingsubstantially pure thiophenols from the hydrocarbon liquid byfractionation.

2. Process in accordance with claim 1 in which the acid oils arefractionated prior to contacting with the water-soluble salt to separatea narrow boiling fraction approximating the boiling point of the purethiophenol to be obtained.

3. The process of preparing a substantially pure thiophenol from acidoils containing the same which are substantially free of alky1mercaptans comprising fractionating the acid oils to obtain a narrowboiling fraction which boils somewhat above and somewhat below theboiling point of the pure thiophenol, contacting the narrow boilingfraction with water soluble salt of mercury whereby to precipitatemercury-thiophenol compound, separating said precipitated compound,dispersing the separated compound in a hydrocarbon liquid boiling belowthe boiling point of the thiophenol, acidifying the dispersion withhydrogen sulfide to precipitate mercury-sulfide and to free thiophenolas a solution in said hydrocarbon liquid and separating the thiophenolfrom the hydrocarbon liquid.

4. Process in accordance with claim 3 in which the substantially purthiophenol is o-thiocresol and the narrow boiling fraction boils fromabout 174 C. to 214 C.

5. Process in accordance with claim 1 in which the precipitated saltsare purified by functional aqueous alcohol solution and crystailizingthe dissolved salts therefrom by cooling the solution, suspending thecrystallized salts in a low boiling hydrocarbon liquid from whichthiophenols can be readily separated, contacting the suspension withhydrogen sulfide until precipitation of mercury as sulfide is completeand separating the liberated thiophenols from the dispersing liquid.

GEORGE W. AYERS, JR. MEYER S. AGRUSS. RICHMOND T. BELL.

